linux-kernel - Re: [PATCH v5 14/19] KVM:VMX: Set host constant supervisor states to VMCS fields

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Date:   Fri, 4 Aug 2023 16:23:47 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <peterz@...radead.org>,
        <john.allen@....com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
        <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v5 14/19] KVM:VMX: Set host constant supervisor states to
 VMCS fields

On Thu, Aug 03, 2023 at 12:27:27AM -0400, Yang Weijiang wrote:
>Set constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} VMCS
>fields explicitly. Kernel IBT is supported and the setting in
>MSR_IA32_S_CET is static after post-boot(except is BIOS call
>case but vCPU thread never across it.), i.e. KVM doesn't need
>to refresh HOST_S_CET field before every VM-Enter/VM-Exit
>sequence.
>
>Host supervisor shadow stack is not enabled now and SSP is not
>accessible to kernel mode, thus it's safe to set host IA32_INT_
>SSP_TAB/SSP VMCS fields to 0s. When shadow stack is enabled for
>CPL3, SSP is reloaded from IA32_PL3_SSP before it exits to userspace.
>Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/SYSRET/SYSENTER SYSEXIT/
>RDSSP/CALL etc.
>
>Prevent KVM module loading and if host supervisor shadow stack
>SHSTK_EN is set in MSR_IA32_S_CET as KVM cannot co-exit with it
>correctly.
>
>Suggested-by: Sean Christopherson <seanjc@...gle.com>
>Suggested-by: Chao Gao <chao.gao@...el.com>
>Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>